ACL race main bearings are manufactured with a tri-layer metal in order to withstand high RPM conditions, high stress loads, and high temperatures. Each ACL race bearing design features the following:

* Large chamfer to accomodate larger crankshaft fillets
* 3/4 groove main bearings to optimize bearing load carrying capacity and oil flow to rod bearings
* Incresed crush and tighter wall tolerance for better seating
* Improved overlay and reduced thickness for increased fatigue strength
* Hardened steel backing to maintain crush under high loads and temperatures

HX Bearings are normally used on race cars. They Expand with heat to allow for better oil flow. Can be used on street cars also, just not necessary.